In the printing and recording arts, it has been known for some years to deliver ink to the printing or recording pen through small conduits. More particularly, this type of ink delivery system has found special application in ink jet printers and in capillary-type recording pens. In such systems, it occasionally occurs that gases evolve from the ink during operation or during periods of shutdown which can cause flow reductions or outright blockage of ink flow during subsequent operation. Also, the ink may evaporate away from the ink jet or pen outlet, so that the writer is not ready to perform when just actuated, but must await movement of ink back to the outlet. Numerous attempts have been made to overcome the problem of gas evolution in the printing ink by means such as improved ink chemistries and various apparatus for removing gas bubbles from the ink as they form. Various caps have been provided to reduce evaporation. While these approaches have achieved a degreee of success, a need has continued to exist for a simple, reliable priming system which can be used to ensure that the ink lines leading to the ink jet or other pen are filled with ink and free of air bubbles at the time the printer is started.